1. Field of the Invention
Embodiments of the present invention generally relate to the fabrication of integrated circuits and to the fabrication of photomasks useful in the manufacture of integrated circuits.
2. Description of the Related Art
Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago. Since then, integrated circuits have generally followed the two year/half-size rule (often called Moore's Law), which means that the number of devices on a chip doubles every two years. Today's fabrication plants are routinely producing devices having 0.15 μm and even 0.13 μm feature sizes, and tomorrow's plants soon will be producing devices having even smaller geometries.
The increasing circuit densities have placed additional demands on processes used to fabricate semi-conductor devices. For example, as circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to sub-micron dimensions, whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Reliable formation of high aspect ratio features is important to the success of sub-micron technology and to the continued effort to increase circuit density and quality of individual substrates.
High aspect ratio features are conventionally formed by patterning a surface of a substrate to define the dimensions of the features and then etching the substrate to remove material and define the features. To form high aspect ratio features with a desired ratio of height to width, the dimensions of the features are required to be formed within certain parameters, which are typically defined as the critical dimensions of the features. Consequently, reliable formation of high aspect ratio features with desired critical dimensions requires precise patterning and subsequent etching of the substrate.
Photolithography is a technique used to form precise patterns on the substrate surface. The patterned substrate surface is etched to form the desired device or features. Photolithography techniques use light patterns and resist materials deposited on a substrate surface to develop the patterns on the substrate surface prior to the etching process. In conventional photolithographic processes, a resist is applied on the layer to be etched, and the features to be etched in the layer, such as contacts, vias, or interconnects, are defined by exposing the resist to a pattern of light through a photolithographic reticle having a photomask layer disposed thereon. The photomask layer corresponds to the desired configuration of features. A light source emitting ultraviolet (UV) light or low X-ray light, for example, may be used to expose the resist to alter the composition of the resist. Generally, the exposed resist material is removed by a chemical process to expose the underlying substrate material. The exposed underlying substrate material is then etched to form the features in the substrate surface while the retained resist material remains as a protective coating for the unexposed underlying substrate material.
Photolithographic reticles typically include a substrate made of an optically transparent material, such as quartz (i.e., silicon dioxide, SiO2), having an opaque light-shielding layer of metal, typically chromium, disposed on the surface of the substrate. The light-shielding layer is patterned to correspond to the features to be transferred to the substrate. Generally, conventional photolithographic reticles are fabricated by first depositing a thin metal layer on a substrate comprising an optically transparent material, such as quartz, and depositing a resist layer on the thin metal layer. The resist is then patterned using conventional laser or electron beam patterning equipment to define the critical dimensions to be transferred to the metal layer. The metal layer is then etched to remove the metal material not protected by the patterned resist, thereby exposing the underlying material and forming a patterned photomask layer. Photomask layers allow light to pass therethrough in a precise pattern onto the substrate surface.
During processing, endpoint data from the patterns disposed on the photolithographic reticles may be used to determine whether the process meets the desired recipe. Each photolithographic reticle generally has its own set of patterns. Consequently, different photolithographic reticles operating under the same recipe generally yield different endpoint data, thereby making it difficult to determine whether the processing conditions in the chamber meet the desired recipe.
Therefore, a need exists in the art for an improved apparatus and method for generating endpoint data that would be consistent for each photolithographic reticle.